1. Field of the Invention This invention relates to a metal roof construction. In one of its aspects, the invention relates to a relatively strong metal roof construction of relatively flat panels with substantially vertical upstanding side walls wherein conventional caulking is used at the ends of the roof and between overlapping panels.
2. Description of the Prior Art
Metal roof constructions have been used for many years on buildings of various sizes and shapes. Most recently, metal roofs have been used on commercial buildings having slightly sloped roofs because of the durability, strength and ease of assembly of these constructions.
Typically a metal roof construction will be formed from a plurality of metal panels joined together at the edges through a batten strip of other means at the side walls. Clips positioned between adjacent panels are secured to supporting purlins and retain portions of the side walls to secure the panels to the purlins. Examples of basic metal roof constructions are disclosed in the U.S. patents to Herberling, U.S. Pat. No. 364,251, issued June 7, 1887, Perry, U.S. Pat. No. 1,240,773, issued Sept. 18, 1917, and Hayman, U.S. Pat. No. 1,693,274, issued Nov. 27, 1928.
Metal roof panels are fairly strong but are subject to buckling under high winds as, for example, hurricane or gale force winds. These winds tend to produce an upward force or lift on the roof structure. When the metal fasteners are strong enough to hold the panels at the edges thereof, the central portions of the panels are forced upwardly and the sides of the panels are thereby drawn inwardly at the base of the upstanding side walls. When the elastic limit of the metal is exceeded, the panels will deform at the upstanding side walls to permit the sides of the panels to move inwardly to accommodate the upward force at the panel centers. Certain standard strength tests have actually been developed by Underwriters Laboratories, Inc. to rate the strength of various roof systems. Insurance rates for building are set in part by the Underwriters Laboratory rating for the roofs.
Various techniques have been employed to strengthen the roof panels to avoid failure from high winds and the like. Obviously, the gauge of metal used can be increased. However, thicker gauge metal will increase the cost as well as the weight of the roof. Strengthening the panels while maintaining a relatively light gauge of metal has included modifying the side walls of the panels so that the panels are spaced apart at the bottom portions thereof. Secondly, corrugations of various sizes and shapes have been provided in the central portions of the panels. Examples of such roof constructions are illustrated in the U.S. patent to Eason, U.S. Pat. No. 2,234,799, issued Mar. 11, 1941, Webb, U.S. Pat. No. 3,520,100, issed July 14, 1970, Day et al, U.S. Pat. No. 3,858,373, issued Jan. 7, 1975. Other examples of roof constructions currently in existence are disclosed in a Butler Manufacturing Company publication entitled "Standing Seam Roof Comparison Chart."
These techniques tend to strengthen the roofs but create other problems. The corrugations create gaps between the panels and supports at the eaves and at the ridges. Special insulation must be provided at such places to seal the roofs. This special insulation increases the cost and decreases the ability to tightly seal the roofs and panels at the edges. Further, corrugations tend to reduce the aesthetic appeal of the roof and make it harder to walk on for repair and installation.